Many automatic analysis devices are known in which one or more liquid samples are introduced into a reagent-carrying rotor. Rotation of the rotor causes the displacement of the liquids to be analyzed towards the cells containing the reagents. Changes of the optical characteristics in the cells where the reaction takes place (changes in opacity, light absorption, color, refraction index, etc.) are measured. In this way, a series of measurements can be obtained which make possible the analysis of one or more samples.
In fact, older devices utilized cells mounted in series or in a descending series on a common support (sample cells, reagent cells, reaction cells) in which the sample moves from one cell to the other by any appropriate means, for example, by gravity. Several reagents and successive reaction cells can be utilized in this way. The proposal was then made to radially arrange these supports on a rotor to make use of the centrifugal force for the purpose of displacing the liquids (samples and possibly reagents) but each elementary support remained independent.
Rotors were conceived on which a series of supports with one or more radial series of cells were placed (see European application Nos. 0 052 769 and 0 052 770 Boehringer Mannhein, for example). Also rotors without separate supports were used but provided for the introduction of the common central inlet followed by separated radial cells (see, for example, U.S. Pat. Nos. 3,744,975 Mailen and 3,798,459 Anderson). But most of these devices often only provided mediocre measurements as a result of nonuniformity of the dosages.
In one form of such centrifugal analyzers, dry reagents are held in small disposable cells located peripherally in a small disposable plastic rotor. The cells have optically clear top and bottom windows. Previously conditioned samples (typically of body fluids such as plasma or urine) are introduced into a receptacle in the center of the rotor. Since many of the reactions with the reagents are time dependent, it is required that the body fluids do not reach the reagents until desired. Centrifugal force is used to transfer the body fluids to the peripheral cells for analysis. To accomplish this transfer, the rotor is accelerated causing the body fluids to move centrifugally out to the cells and reagents. After a prescribed time the color changes are read optically to determine the results of the test. Since many cells (each with different reagents to perform a separate analysis) can be positioned in each rotor, the result is a fairly complete chemistry of the body fluid in a compact unit in a relatively short period of time.
Typical of these rotors are those described in U.S. Pat. Nos. 4,123,173, 3,555,284 and 4,387,164. While quite satisfactory for their intended purposes these rotors do not fulfill the need that exists for a small disposable rotor that is capable of accurately providing many tests on a single sample. Disposable rotors of this type are described in a series of patents issued to Guigan. Typical of these patents are U.S. patent application Ser. No. 626,749 filed July 2, 1984 and U.S. Pat. No. 4,154,793. These rotors are comprised of two disk-like rigid plastic pieces secured together to form a closed rotor. The lower disk has a central hub for mounting on a rotor drive shaft and comprises a flat disk having a central receptacle and a plurality of peripheral cells formed therein. Each cell is separated from an adjacent cell by a raised radial ridge which forms sectors for each cell. A radial groove of capillary thickness dimensions extends from the central receptacle formed in the lower disk to the center, radially inner portion of each cell.
The top disk has a flat lower surface which is sealed to the radial ridges and periphery of the lower disk so as to provide the closed rotor. The rotor thus defines a plurality of small sectors each with a slit of capillary dimensions communicating with each cell from the central cavity. This rotor is a disposable unit adapted to receive a patient sample, through an opening in the center portion of the upper disk, which is retained in the central receptacle. The sample when subjected to centrifugal force is preferentially driven by the combined action of centrifugal force and capillary action to each sector to fill each cell. Air escapes from each cell through the groove formed in the lower disk.
One problem inherent in the Guigan design is that different chemistries, different dilutions or different fluids are necessary; therefore, more than one central well is required. This is typically accomplished by placing a baffle in the central receptacle. Without the baffle all cells are subjected to the same pressure. With the baffle in the central cavity, due to acceleration, the cells nearest the leading edge of the baffle tend to be filled first. Also, it is sometimes difficult to fill all of the cells completely since the groove tends to become filled with liquid trying to exit the central receptacle under centrifugal force. This can result in filling differences and difficulty of completely filling a particular cell with fluid from the central receptacle.